The fire broke out on Dec. 6 just before 5 a.m. at an encampment under Interstate 405 and Sepulveda Boulevard in Long Beach , the fire department said. The fire was then spread by arid landscapes and Santa Ana winds, which also fueled five other fires throughout the state last week.

No one was present when authorities arrived at the area of origin, and no arrests have been made in connection with the fire, officials said.

The Skirball fire burned more than 400 acres and destroyed six homes and damaged 12 others in Bel-Air, the fire department said. As of Tuesday, it was 85 percent contained, but dozens of firefighters continued to work to achieve 100 percent containment, according to fire officials.

Last week, the Skirball fire caused all Los Angeles Unified School District schools in the San Fernando Valley and 17 schools on Los Angeles’ Westside to shutter due to the poor air quality, officials said. All evacuations due to the Skirball fire have now been lifted.

About 90 percent of wildfires in the U.S. are human-caused, according to the National Park Service. The fires are often caused by campfires that are left unattended, the burning of debris, cigarettes that are discarded negligently, and intentional acts of arson, the National Park Service said. The remaining 10 percent of wildfires are caused by lightning or lava, according to the park service.

Five fires are still blazing through the Golden State.

The Thomas fire, threatening more than 18,000 structures in Santa Barbara and Ventura counties, remains the main concern for firefighters at just 20 percent containment.

More than 6,000 fire personnel are still battling the Thomas fire, which has singed through more than 234,000 acres so far, growing by more than 50,000 acres on Sunday alone. The Thomas fire has destroyed nearly 800 structures and damaged at least 187, according to the California Department of Forestry and Fire Protection.

Severe fire weather will continue to promote significant fire growth in Santa Barbara County, the Department of Fire said.

The remaining fires, the Lilac, Creek and Rye fires, were all at least 92 percent contained as of Tuesday afternoon, officials said.